1. Field of the Invention
The present invention relates to an image forming apparatus and a detecting method of a pattern image regarding image quality adjustment.
2. Description of the Related Art
Conventional image forming apparatuses form images by forming the images on the image carriers such as transfer belts and transferring the images to recording media such as paper (hereinafter, “paper”). The image forming apparatuses form pattern images for detection on the image carriers, judge output values obtained by reading the pattern images by the sensors using predetermined thresholds to detect the pattern images, and perform image quality adjustment such as concentration adjustment of and positional adjustment of images to be formed on paper based on the detected pattern images.
The sensors used for the image quality adjustment may be subjected to aged deterioration such as contamination due to dust or the like and thus their output values may fluctuate. Therefore, the output of the sensors is previously detected to adjust a light amount while pattern images are read during the image quality adjustment. Moreover, other image forming apparatuses form predetermined reference images on the image carriers and determine thresholds used when pattern images are read, based on the reading result of the reference images (see Japanese Patent Application Laid-open No. 2001-324847, Japanese Patent Application Laid-open No. 2003-131443, and Japanese Patent Application Laid-open No. 2004-213032).
A margin of the light amount adjustment when pattern images are read is limited by specified upper limit of driving current of a light-emitting element or similar limitation. However, the conventional art described above determines thresholds used when pattern images are read without consideration of the limitation of the light amount adjustment, and therefore, is not sufficient to perform pattern detection in response to aged deterioration such as contamination of a sensor.